RF power amplifiers used for wireless communication transmitters require high linearity to preserve modulation accuracy and to limit spectral regrowth. Linear amplifiers are capable of electrical (DC power in to RF power out) efficiencies greater than fifty percent when operated at saturation. However, they are generally not operated at an optimal level of efficiency due to the need to provide high linearity. For constant envelope waveforms, linear amplifiers are often operated below saturation to provide for operation in their linear region. Time varying envelopes present an additional challenge.
One technique for enhancing the efficiency of an amplifier system is Envelope Elimination and Restoration (EER). The EER technique detects the envelope of the incoming signal to produce an amplitude modulated (AM) component of the incoming signal and a phase modulated (PM) component with a constant envelope. The PM signal component is provided to the input of the power amplifier along a PM path and the AM component is employed to modulate the supply of the power amplifier along an AM path. Since the signal input into the power amplifier has a constant amplitude envelope, a more efficient class of power amplifier can be employed to amplify the input signal. Additionally, since the supply signal changes with the desired power of the amplified signal, the amplifier can be operated at compression enhancing the efficiency of the amplifier.